Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-04-09
2003-11-11
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S193000, C526S217000, C526S328000, C526S346000, C525S255000, C525S259000, C525S299000, C564S015000, C564S300000, C564S301000, C252S182120, C252S182140, C252S182230
Reexamination Certificate
active
06646079
ABSTRACT:
The invention relates to a process for the preparation of polymers with the distribution of multimodal molecular masses (“multimodal polymer”) by controlled radical polymerization.
A distribution of molecular masses is said to be multimodal when it comprises several groups of molecules with different average molecular masses. This may be reflected by the existence of a simple shoulder on the flank of the main peak or by the existence of several maxima in the curve obtained by gel permeation chromatography (GPC).
A polymer comprising two groups of molecules with different average molecular masses is said to be bimodal (bimodal polymer). A polymer comprising three groups of molecules with different average molecular masses is said to be trimodal (trimodal polymer).
The manufacture of multimodal polymers is a basic challenge in the field of materials as polymers of this type make it possible to combine, in the same material, the properties of each group of molecules from which it is composed. For example, polymers of high mass introduce good mechanical strength, whereas low masses make it possible to retain, in the material, good fluidity at high temperature, which facilitates its processing.
A particular goal is techniques for the preparation of bimodal polymers. This is because the preparation of such polymers is of use as these polymers generally exhibit both, first, good mechanical properties, in particular impact strength (measured by the Izod and/or Charpy test, ISO Standard 180 and ISO Standard 179 respectively), and better behaviour at high temperatures, which is reflected by a high Vicat point and a higher heat deflection temperature or HDT (Vicat: ISO Standard 306, HDT: ISO Standard 75), the said good mechanical properties deriving in particular from the population with high molecular masses, and, secondly, are easy to process, in particular by conversion technologies known to a person skilled in the art (extrusion, injection moulding, transfer compression moulding, thermoforming), due in this instance to the presence of the population with low molecular masses, the latter in fact acting as plasticizer.
In the field of radical polymerization, a known technique for manufacturing such polymers consists in carrying out two successive polymerizations: the first polymerization produces the polymers of low mass, which act as reaction medium for the manufacture of the second family of polymers of high mass (see EP 905153, EP 905151, EP 881237). The disadvantage of such a technique is that it is necessary to have two reactors “in cascade”, which involves a large capital cost. Another technique consists in melt blending two resins but the choice of the blends is restricted by the miscibility of the resins. Finally, a third technique consists in partially grafting, to a polymer, another type of polymer, which here again requires a multistage process.
EP 905 151 discloses a technique for producing bimodal polyethylene. U.S. Pat. No. 5,723,554 (from the same family as GB 2 304 721) discloses the preparation of polystyrene with a narrow polydispersity by polymerization of styrene in the presence of stable radicals of nitroxyl type and in the presence of divinylbenzene.
The crosslinking of polymers by a coupling agent in order to obtain networks and gels is described in Polymer Preprints, vol. 40, No. 2, page 366, August 1999 (Chaumont et al).
U.S. Pat. Nos. 5,627,248, 5,498,679 and 4,581,429 disclose the use of a polyalkoxyamine for the synthesis of polymers by polymerization controlled by nitroxides. These three patents describe the use only of one polyalkoxyamine at the same time. In these documents, the base common to the alkoxyamine is the TEMPO radical. These patents relate essentially to the controlled radical polymerization of styrene and its derivatives, since the alkoxyamine used is not suitable for the polymerization of other types of monomer. In U.S. Pat. No. 5,627,248, mixed alkoxyamine-azo compounds are disclosed but the use of a mixture of alkoxyamine and of conventional peroxide or azo initiators is not mentioned in this document.
The following documents may also be mentioned: U.S. Pat. No. 4,581,429, WO 96/24620, French Patent Application No. 99 00127, French Patent Application No. 99 06329, French Patent Application No. 99 04405, French Patent Application No. 99 01998, French Patent Application No. 98 12477 (published under No. FR 2 784 111) and T. Fukuda et al., Macromolecules, 1996, 29, 6393.
The invention makes possible the manufacture of multimodal polymers in a single stage by virtue of the use of specific alkoxyamines. Each group of polymer molecules is obtained in a controlled manner, which means that each peak in the mass distribution can be very fine and that the ratios of the masses of each family to one another are controlled. The technique is particularly suited to the preparation of block copolymers.
The process according to the invention is a controlled radical polymerization process. The control of a radical polymerization improves in proportion as the curve representing the change in the number-average molecular mass (Mn) as a function of the conversion of monomer to polymer approaches linearity. Likewise, the control of a radical polymerization improves in proportion as the curve representing the change in the Napierian logarithm of the M
o
/M ratio (M
o
representing the initial concentration of monomer and M representing the concentration of monomer at a given instant during the polymerization) as a function of time approaches linearity.
It is by virtue of the fact that a radical polymerization process is controlled, for example by a stable free radical, that the said process makes possible the preparation of block polymers by successive introduction of different monomers into the polymerization medium. This is because, by virtue of such a process, the polymer in the course of formation is a living polymer.
The process according to the invention makes it possible to prepare multimodal polymers which are well controlled in terms of ratio of the masses of the various populations and in terms of accuracy of the chain lengths, this preparation being carried out by a very simple process involving conventional polymerization techniques used for a monomodal polymer (a single population of molecules). In addition, the living nature of the polymerization makes it possible to prepare multimodal copolymers. Products which are better defined and more varied than those obtained by the processes of the prior art are thus obtained in a conventional reactor with kinetics which are better defined.
According to the prior art, the stable radicals used are mainly from the family of 2,2,6,6-tetramethyl-1-piperidinyloxy (commonly known as “TEMPO”), which can be represented by:
The alkoxyamines derived from TEMPO, and thus of the type:
in which R represents, for example, an alkyl radical, are capable of initiating and of controlling polymerizations. However, the kinetics of these polymerizations are not a function of the initial concentration of alkoxyamines. Thus, in such systems, operating with twice as much initiator does not make it possible to multiply by two the conversion as a function of time. In this case, the use of a dialkoxyamine, such as:
provides the same curve of conversion as a function of time as that obtained with a monoalkoxyamine, such as:
It is probable that the very high importance of thermal initiation in these systems is the cause of this effect.
There is therefore great importance in using alkoxyamines for which the initial concentration is directly related to the kinetics of conversion as it makes it possible to obtain a polymer with a weight-average molecular mass of 100 000 g/mol from a dialkoxyamine in a time equal to that necessary to synthesize a polymer with a weight-average molecular mass of 50 000 g/mol from a monoalkoxyamine. It is by virtue of this discovery that it is possible, in the context of the invention, to prepare controlled (and living) polymers exhibiting a bi- or multimodal distribution of masses by simple polymerizati
Gnanou Yves
Guerret Olivier
Robin Sophie
Atofina
Millen White Zelano & Branigan P.C.
Teskin Fred
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